The present invention is directed to a control board for a dental apparatus that contains a control panel having a plurality of key surfaces for the actuation of sensor means that respond to a force or change in force.
In prior art control boards of this type, the control panels are predominantly executed in foil technique wherein foil keyboards are positioned on a carrier surface or are also glued behind a frame. For example, a control panel of this type is known from the Company Brochure "KaVo-SYSTEMATICA 1062" No. WTE-PR-NO. 829712 VI 91 of Kaltenbach & Voigt, Biberach. In such an arrangement an edge gap always occurs in which dirt and moisture can collect. Added thereto is that cleaning and disinfection of the surface is relatively difficult to carry out. A further disadvantage is that the foil keyboard can be relatively easily damaged.
European reference EP-A1-0 366 832 discloses a rigid plate of metal (aluminum or brass) or wood arranged over a foil keyboard in order to protect it. The rigid plate is so thick that the foil keyboard lying therebelow cannot be faultlessly actuated given pressure on the plate, whether it is because no key responds or because a plurality of keys simultaneously respond. In order to be able to actuate the keyboard, it is proposed in this reference to provide zones of reduced stiffness in the plate, namely over the respective key regions of the foil keyboard. The zones of reduced thickness can be created by changes in the material properties of the plate at the respective location. Alternatively, recesses can be provided at the corresponding locations, these being open toward the foils and being selected of such a depth that the plate part remaining over the recess has adequate elasticity in order to relay the finger pressure for key actuation onto the key.
U.S. Pat. No. 4,382,165 discloses a keyboard wherein two interconnects containing the switch elements are arranged sandwich-like between two rigid plates.
German reference DE-C2-3 717 325 discloses a transparent, touch-sensitive control panel that has a transparent, touch-sensitive contact region with a plurality of individual contacts arranged in a two-dimensional grid. The contact area is composed of an upper plate of transparent plastic film, a lower plate of a similar, transparent material and an insulating spacer situated therebetween. The contact arrangement is mounted on a base plate that is also composed of transparent plastic.
The principal aim of this control panel is to prevent foreign material being introduced into or enclosed in the light path, in order to assure that the image of the visual display that is seen through the touch-sensitive switch is neither distorted nor interrupted. Further, the formation of Newtonian rings that would form as a result of the air layer between the lower plate and the base plate is to be prevented.